Day 13 part 2.

Author: sraaphorst

src/main/kotlin/day13/day13.kt

@@ -6,6 +6,9 @@ package day13
 import common.aocreader.fetchAdventOfCodeInput
 import common.intpos2d.*
 import common.runner.timedFunction
+import java.math.BigInteger
+
+private typealias BigIntPos = Pair<BigInteger, BigInteger>
 
 data class Machine(val deltaA: IntPos2D, val deltaB: IntPos2D, val prizePos: IntPos2D) {
     /**
@@ -14,21 +17,28 @@ data class Machine(val deltaA: IntPos2D, val deltaB: IntPos2D, val prizePos: Int
      * [dAx  dBx] (a) = (px)
      * [dAy  dBy] (b)   (py)
      */
-    fun calculateSolution(): IntPos2D? {
+    fun calculateSolution(adjustment: BigIntPos): BigIntPos? {
         val determinant = deltaA.x() * deltaB.y() - deltaB.x() * deltaA.y()
         if (determinant == 0) return null
+        val detBigInteger = determinant.toBigInteger()
 
-        val abDet = IntPos2D(
-            deltaB.y() * prizePos.x() - deltaB.x() * prizePos.y(),
-            deltaA.x() * prizePos.y() - deltaA.y() * prizePos.x())
-
-        return if (abDet % determinant != Zero2D) null else abDet / determinant
-    }
+        val adjPx = prizePos.x().toBigInteger() + adjustment.first
+        val adjPy = prizePos.y().toBigInteger() + adjustment.second
+        val abDet = BigIntPos(
+            deltaB.y().toBigInteger() * adjPx - deltaB.x().toBigInteger() * adjPy,
+            deltaA.x().toBigInteger() * adjPy - deltaA.y().toBigInteger() * adjPx)
 
+        val detX = abDet.first % detBigInteger
+        val detY = abDet.second % detBigInteger
 
+        return if (detX == BigInteger.ZERO && detY == BigInteger.ZERO)
+            BigIntPos(abDet.first / detBigInteger, abDet.second / detBigInteger)
+        else null
+    }
 
     companion object {
-        val TokenCost = IntPos2D(3, 1)
+        val TokenCostA = 3.toBigInteger()
+        val TokenCostB = BigInteger.ONE
 
         private val MachineRegex = """[XY][+=](\d+)""".toRegex()
 
@@ -43,17 +53,22 @@ data class Machine(val deltaA: IntPos2D, val deltaB: IntPos2D, val prizePos: Int
 fun parse(input: String): List<Machine> =
     input.split("""[\r\n]{2}""".toRegex()).map { Machine.parse(it.trim()) }
 
-fun answer1(input: String): Int =
+fun answer(input: String, adjustment: BigIntPos = BigIntPos(BigInteger.ZERO, BigInteger.ZERO)): BigInteger =
     parse(input)
-        .mapNotNull(Machine::calculateSolution)
-        .sumOf { it dot Machine.TokenCost }
+        .mapNotNull { it.calculateSolution(adjustment) }
+        .sumOf { sol -> sol.first * Machine.TokenCostA + sol.second * Machine.TokenCostB }
 
-//fun answer2(input: String): Int =
-//    parse(input).let(::findRegions).let(::regionCosts2)
+fun answer1(input: String): BigInteger =
+    answer(input)
+
+private val adjustment2 = BigInteger("10000000000000")
+
+fun answer2(input: String): BigInteger =
+    answer(input, BigIntPos(adjustment2, adjustment2))
 
 fun main() {
     val input = fetchAdventOfCodeInput(2024, 13)
     println("--- Day 13: Claw Contraption ---")
     timedFunction("Part 1") { answer1(input) } // 28262
-//    timedFunction("Part 2") { answer2(input) } // 953738
-}
+    timedFunction("Part 2") { answer2(input) } // 101406661266314
+}

src/test/kotlin/day13/day13.kt

@@ -30,12 +30,6 @@ class Day13 {
 
     @Test
     fun `Problem 1 example`() {
-        assertEquals(480, answer1(input1))
+        assertEquals(480.toBigInteger(), answer1(input1))
     }
-
-//    @Test
-//    fun `Problem2 example`() {
-//        assertEquals(80, answer2(input1))
-//        assertEquals(1206, answer2(input2))
-//    }
 }